Python拉姆达

在Python中，匿名函数意味着函数没有名称。我们已经知道 def 关键字用于定义普通函数，而 lambda 关键字用于创建匿名函数。它具有以下语法：

句法：

lambda arguments : expression

这个函数可以有任意数量的参数，但只有一个表达式，它被计算并返回。
一种是在需要函数对象的地方免费使用 lambda 函数。
您需要了解 lambda 函数在语法上仅限于单个表达式。
除了函数中的其他类型的表达式之外，它在特定的编程领域有各种用途。

示例 #1：

Python3

# Python program to demonstrate
# lambda functions
 
 
string ='GeeksforGeeks'
 
# lambda returns a function object
print(lambda string : string)

Python3

# Python program to demonstrate
# lambda functions
 
 
x ="GeeksforGeeks"
 
# lambda gets pass to print
(lambda x : print(x))(x)

Python3

# Python program to illustrate cube of a number 
# showing difference between def() and lambda().
 
 
def cube(y):
    return y*y*y;
   
g = lambda x: x*x*x
print(g(7))
   
print(cube(5))

Python3

# Python program to demonstrate
# lambda functions
 
 
def power(n):
    return lambda a : a ** n
 
# base = lambda a : a**2 get
# returned to base
base = power(2)
 
print("Now power is set to 2")
 
# when calling base it gets
# executed with already set with 2
print("8 powerof 2 = ", base(8))
 
# base = lambda a : a**5 get
# returned to base
base = power(5)
print("Now power is set to 5")
 
# when calling base it gets executed
# with already set with newly 2
print("8 powerof 5 = ", base(8))

Python3

# Python program to demonstrate
# lambda functions inside map()
# and filter()
 
 
a = [100, 2, 8, 60, 5, 4, 3, 31, 10, 11]
 
# in filter either we use assignment or
# conditional operator, the pass actual
# parameter will get return
filtered = filter (lambda x: x % 2 == 0, a)
print(list(filtered))
 
# in map either we use assignment or
# conditional operator, the result of
# the value will get returned
mapped = map (lambda x: x % 2 == 0, a)
print(list(mapped))

输出：

 at 0x7f268eb16f28>

在上面的示例中，打印函数没有调用 lambda，而是简单地返回函数对象和存储它的内存位置。
所以，为了让 print 首先打印字符串，我们需要调用 lambda 以便字符串通过 print。

示例 #2：

Python3

# Python program to demonstrate
# lambda functions
 
 
x ="GeeksforGeeks"
 
# lambda gets pass to print
(lambda x : print(x))(x)

输出：

GeeksforGeeks

示例 #3： lambda 和普通函数调用之间的区别

Python3

# Python program to illustrate cube of a number 
# showing difference between def() and lambda().
 
 
def cube(y):
    return y*y*y;
   
g = lambda x: x*x*x
print(g(7))
   
print(cube(5))

输出：

343
125

示例 #4： lambda函数在函数内部使用时会变得更有帮助。

Python3

# Python program to demonstrate
# lambda functions
 
 
def power(n):
    return lambda a : a ** n
 
# base = lambda a : a**2 get
# returned to base
base = power(2)
 
print("Now power is set to 2")
 
# when calling base it gets
# executed with already set with 2
print("8 powerof 2 = ", base(8))
 
# base = lambda a : a**5 get
# returned to base
base = power(5)
print("Now power is set to 5")
 
# when calling base it gets executed
# with already set with newly 2
print("8 powerof 5 = ", base(8))

输出：

Now power is set to 2
8 powerof 2 =  64
Now power is set to 5
8 powerof 5 =  32768

我们还可以使用 map() 方法将列表推导式替换为 Lambda，不仅速度快而且效率高，我们还看看如何在 filter() 中使用 lambda。

示例 #5： filter() 和 map(

Python3

# Python program to demonstrate
# lambda functions inside map()
# and filter()
 
 
a = [100, 2, 8, 60, 5, 4, 3, 31, 10, 11]
 
# in filter either we use assignment or
# conditional operator, the pass actual
# parameter will get return
filtered = filter (lambda x: x % 2 == 0, a)
print(list(filtered))
 
# in map either we use assignment or
# conditional operator, the result of
# the value will get returned
mapped = map (lambda x: x % 2 == 0, a)
print(list(mapped))

输出：

[100, 2, 8, 60, 4, 10]
[True, True, True, True, False, True, False, False, True, False]